As is well known, unpolarized light is comprised of light in which the electric vector is randomly oriented; the direction of the electric vector is orthogonal to the direction of propagation of the light. Plane polarized light or linearly polarized light is light in which the electric vector generally is oriented in a single plane. Various means have been used in the past to polarize light, especially to convert unpolarized light to linearly polarized light.
Most, if not all, prior art polarizers provide a fixed amount of polarization. It would be desirable to be able to control polarization of light, i.e., to determine whether light emanating from a polarizer device in response to incident unpolarized light in fact is polarized or unpolarized and if polarized, to what extent polarized. The invention as described further below provides such capability.
The combination of liquid crystal material, for example, nematic liquid crystal or operationally nematic liquid crystal, in a containment medium and methods of making the same are disclosed in U.S. Pat. Nos. 4,435,047, 4,606,611, 4,591,233, 4,707,080 and 4,616,903. In several embodiments disclosed in a number of such patents, pleochroic dye is included in the liquid crystal volumes bounded by the containment medium. In operation, as a function of whether or not the prescribed input is applied, light either is transmitted or light is scattered or absorbed. Absorption primarily is due to the absorption characteristics of the dye; scattering primarily is due to index of refraction considerations.
In U.S. Pat. No. 4,556,289 a combination of liquid crystal and pleochroic dye in volumes formed in a containment medium is disclosed. The liquid crystal has low birefringence characteristics, and the index of refraction thereof is closely matched with that of the containment medium. Therefore, as a function of whether or not a prescribed input is applied, the intensity of light transmitted therethrough can be varied without substantially altering the image characteristics.
The devices disclosed in the above patents are operative substantially independently of optical polarization.
In U.S. Pat. Nos. 4,385,806, 4,436,376, 4,540,243 and Re. 32,521 a surface mode switching technique for liquid crystal to control light in response to electric field applied to liquid crystal is disclosed. Other devices which act as a wave guide to reorient the direction of optical polarization of light are known as twisted nematic liquid crystal devices.
A liquid crystal polarizer is disclosed in U.S. Pat. No. 4,048,358. Such polarizer includes an open micropore structure in a polypropylene sheet with liquid crystal material and dichroic dye in the pores. The pores tend to align the liquid crystal along the axis of the pores.
In U.S. Pat. Nos. 4,688,900, 4,685,771, 4,671,618 and 4,673,255 are disclosed liquid crystal devices in which volumes of liquid crystal material are formed in a containment medium. The patents disclose formation of such volumes of such liquid crystal material by condensation or spontaneous formation techniques. Application of stress to deform the volumes to form a polarizer and index of refraction considerations also are disclosed. Further, a switchable polarizer is mentioned in U.S. Pat. No. 4,688,900.
The entire disclosures of the above patents hereby are incorporated by reference.